Agitator mill

ABSTRACT

An agitator shaft (22) is diposed in a milling body (12) which includes a grinding chamber (18) to be filled at least partly with grinding media (50) and material (52) to be ground and has an inlet for material to be ground and an outlet for crushed material. The agitator shaft (22) has an end portion (38) in which a cavity (40) is formed which is open at the inner shaft end. The end portion (38) comprises recesses (46) all around the cavity (40) to permit grinding media (50) to flow off which entered the cavity (40) through the inner shaft end. A separating means (42) is arranged inside the cavity (40) to permit finished pulverized material (52) to flow out of the grinding chamber (18) to the outlet (30) while it retains grinding media (50). In this manner the separating means (42) is effectively protected from any direct impact of activated grinding media (50). And yet the risk is avoided that the separating means (42) becomes clogged, by virtue of the rotation of the agitator shaft (22).

The invention relates to an agitator mill comprising

a milling body which includes a grinding chamber to be filled at leastpartly with grinding media and material to be ground and has an inletfor material to be ground and an outlet for crushed material,

an agitator shaft having an inner shaft end inside the grinding chamber,

and a separating means permitting finished pulverized material to flowout of the grinding chamber to the outlet, yet retaining grinding media.

In a known agitator mill of this kind (DE-PS No. 2 037 358) designed asan upright agitator mill, including a vertical agitator shaft theseparating means consists of a plurality of screen cartridges disposedin the upper region of the grinding chamber. In one embodiment (FIGS. 1and 2) the grinding chamber is connected by three parallel horizontaltubes to the outlet for pulverized material flange-mounted laterally tothe milling body. Through each of these tubes a screen cartridge isintroduced into the grinding chamber such that one of the screencartridges extends radially to the agitator shaft, terminating justshort of the same, while two other ones which are longer are disposed ateither side of the agitator shaft. In another embodiment (FIG. 3) screencartridges are arranged offset with respect to one another in parallelwith the agitator shaft and communicate with an outlet for pulverizedmaterial located above the grinding chamber. In both cases the flow ofgrinding media and material to be ground circulates well all around thescreen cartridges so that they do not become clogged. Yet in operationthe screen cartridges are constantly hit by grinding media activateddirectly by the agitator shaft and thus impacting at great energy ofmotion on the screen cartridges which, therefore, are subject to quickwear.

It is, therefore, the object of the invention to design an agitator millsuch that the separating means is largely withdrawn from the grindingmedium activated directly by the agitator shaft and yet does not tend tobecome clogged.

This object is met, in accordance with the invention, in an agitatormill of the kind specified initially in that

the agitator shaft has an end portion formed with a cavity which is openat the inner shaft end,

the end portion of the agitator shaft includes recesses which aredistributed around the cavity and spaced from the inner shaft end andpermit grinding media which entered the cavity through the inner shaftend to flow back into the grinding chamber,

and the separating means is arranged at least substantially inside thecavity.

The invention has the advantage of the separating means, no matter whatits particular structure may be, being arranged protectedly within theopen-ended cavity formed in the end portion of the agitator shaft,whereby grinding medium activated directly by the agitator shaft hardlyhas a chance to collide with the separating means. And yet the risk ofobstruction of the separating means is avoided by the rotation of theagitator shaft.

Preferably at least one conveying member is formed at the agitator shaftfor enhancing the axial flow of the grinding medium and material to beground from the inner shaft end through the cavity to the recesses. Theconveying member may be constituted by the wall itself of the cavity,for instance by conical enlargement of the cavity away from the innerend of the shaft.

The separating means preferably is disposed at least approximatelycoaxially with the agitator shaft. It may also be convenient to disposethe separating means parallel or at an angle with respect to the axis ofthe agitator shaft, depending on the position of the agitator shaft inspace and on the type and properties of the material to be ground.

The separating means may be arranged on a tube which extends throughpart of the grinding chamber from the inner shaft end into the cavity.This embodiment of the invention permits particularly easy assembly anddisassembly of the separating means together with the tube.

Conveniently the tube is guided so as to be pulled out to the exteriorin a tubular socket which extends from an end face of the milling bodyinto the cavity.

It is likewise advantageous if the tube is guided for being pulled outto the exterior in a sleeve which is disposed at an end wall of themilling body for adjustment between a normal operating position at whichit is located substantially outside of the grinding chamber and aposition for exchange of the separating means, at which position thesleeve protrudes into the cavity and sealingly engages the agitatorshaft in a manner so as to retain the grinding medium.

In another embodiment of the invention the separating means, regardlessof its specific structure, communicates through the altogether hollowagitator shaft with the outlet for crushed material located at an outershaft end.

As with the known agitator mill described initially, also the separatingmeans of the subject matter of the invention may comprise a tubularscreen cartridge. In this case the separating means may be fixed to theagitator shaft and rotate together with the same.

With alternative embodiments of the invention the separating meanscomprises two per se known separating discs which are disposed coaxiallywith the agitator shaft and define an annular gap, one of saidseparating discs being rotatable and the other one being disposedstationarily.

The invention will be described further, by way of example, withreference to diagrammatic drawings, in which:

FIG. 1 is a side elevational view of an horizontal agitator mill;

FIG. 2 is an enlarged axial sectional view of part of the agitator mill;

FIG. 3 is the cross sectional view III--III of FIG. 2; and

FIGS. 4 to 14 are modifications of FIG. 2.

The horizontal agitator mill shown in FIGS. 1 to 3 comprises a box-likeframe 10 on which a substantially cylindrical milling body 12 is fixedas well as a bearing casing 14 axially adjacent the same. The frame 10contains a drive motor (not shown) and is connected to the bearingcasing 14 by a transmission casing 16 in which a gear (likewise notshown) is housed having an adjustable transmission ratio.

The milling body 12 has a circular cylindrical grinding chamber 18 inwhich an agitator 20 is received. The agitator 20 substantially consistsof an agitator shaft 22 supported in the bearing casing 14 and extendingcoaxially with the milling body 12 through almost the entire grindingchamber 18 and of a number of rod-shaped agitating members 24 fixed tothe agitator shaft 22 at equal axial spacings and protruding into spacesbetween counter-rods 26 fixed to the milling body 12.

An inlet 28 for material to be ground is disposed at the left end of themilling body 12. In operation a suspension or slurry of material to beground and liquid is pumped continuously through this inlet into thegrinding chamber 18.

An outlet 30 for finished,crushed material is arranged at the end faceof the milling body 12 remote from the inlet 28, being the right endface in FIGS. 1 and 2. Finished, crushed material is constantly pumpedout through this outlet. The outlet 30 is formed by a threaded socket atthe end of a tube 32 to which a flange 34 is fixed. The flange 34 isconnected threadedly with a cover constituting an end wall 36 of themilling body 12 at the side remote from the transmission casing 16.

The tube 32 extends through the end wall 36, in the embodiment showncoaxially with the agitator shaft 22, and passes through the adjacentarea of the grinding chamber 18 up to an end portion 38 of the agitatorshaft 22. The end portion 38 is releasably screwed together with themain portion of the agitator shaft 22 and comprises a cavity 40 which isopen at the end face and in which a separating means 42 is arranged.

With the embodiment illustrated in FIGS. 1 to 3 the separating means 42is formed by a cylindrical screen cartridge which has the same diameteras tube 32 and is formed integral with the same. The separating means 42extends coaxially with the agitator shaft 22 across the major part ofthe length of the cavity 40 and has a closed end 44 the spacing of whichfrom the axially inner end of the cavity 40 as well as the radial widthof the annular space between the cylindrical portion of the screencartridge and the inner wall of the end portion 38 correspond toapproximately 15 to 20% of the diameter of the cavity 40.

Slot-like recesses 46 are formed in parallel with the axis in the endportion 38 and each have a cross sectional shape of a circular ringsector. They extend across the major part of the length of the cavity 40so that the screen cartridge 42 is surrounded by these recesses almostfor its entire length. In cross section, as seen in FIG. 3, the recessesextend like circular ring sectors across an angular range each of 45°,leaving webs 48 between them which have the same cross section so thatthe end portion 38 as a whole is similar to a cylindrical cage which isopen at one end face. Three of the rod-shaped agitating members 24 eachare fixed to each web 48 so that the end portion 38 is fully comparablewith the main portion of the agitator shaft 22 as far as the equipmentwith agitating members is concerned.

In operation the agitator shaft 22 rotates at a speed which is customaryin agitator mills and lies in the range of, for instance, from 200 to3000 r.p.m., depending on the diameter of the agitator shaft and thecharacter of the material to be ground. Hereby the mixture contained inthe grinding chamber 18 of grinding media 50 and material to be groundis activated. A pumping means (not shown) produces low pressure in thetube 32 by means of which grinding media and material 52 to be groundare permitted to flow from the grinding chamber 18 into the cavity 40.The finished, crushed material passes through the screen cartridge 42into the tube 32, whereas grinding media are retained and flow back intothe grinding chamber 18 through the recesses 46. The return flow ispromoted by centrifugal forces resulting from the influence of the webs48 and the agitating members 24 fixed to the same, acting on thegrinding media 50.

FIG. 4 shows a simplified axial section of an embodiment in which theseparating means 42 likewise is embodied by a screen cartridge andarranged in the cavity 40 of the end portion 38 of the agitator shaft22. However, here the separating means 42 is fixed to the end of a tube54 extending within the altogether hollow agitator shaft 22 through thebearing casing 14 (FIG. 1) where it is connected to an outlet forcrushed material which replaces the outlet 30 shown for crushedmaterial.

The embodiments shown in FIGS. 5 and 6 are similar in overallarrangement to FIG. 2. Again the separating means 42 is disposed at atube 32 which extends through part of the grinding chamber 18. Yet theseparating means 42 is embodied by two annular separating discs 56 and58 arranged coaxially with the agitator shaft 22 and defining acylindrical annular gap 60 between them. The separating disc 56 issecured to the agitator shaft 22 and rotates together with the same; theseparating disc 58 is secured to the tube 32, thereby being stationary.

According to FIG. 5 the stationary separating disc 58 is disposedradially outwardly and the rotatable separating disc 56 radiallyinwardly; the opposite is the case in FIG. 6.

FIG. 7 shows a modification which differs from FIGS. 5 and 6 in that thetwo separating discs 56 and 58 have approximately the same size and arepositioned axially opposite each other so that they define asubstantially planar radial annular gap 60. The separating discs 56 and58 also could be conical, defining between them a likewise conicalannular gap.

FIGS. 8 and 9 show two further embodiments with which the separatingmeans 42 likewise formed by two separating discs 56 and 58 does notinclude a structural member which rotates together with the agitatorshaft 22. The rotatable separating disc 56 is secured to a shaft 62arranged coaxially with the agitator shaft 22 inside the tube 32 andadapted to be driven by a motor 64 of its own which is flange-mounted onthe end wall 36. The stationary separating disc 58 each is fixed to thetube 32, radially outside of the rotating disc 56 in FIG. 8 and axiallynext to the same in the case of FIG. 9.

As shown in FIG. 10, a conveying member 66 in the form of a helix isarranged around the separating means 42 which again is embodied by ascreen cartridge. It is fixed to the end portion 38 of the agitatorshaft 22 within the cavity 40.

The helix is so designed that the conveying member 66 feeds grindingmedia 50 and material 52 to be ground within the cavity 40 away from theopen end thereof, i.e. to the left in FIG. 10 when the agitator shaft 22is driven in the direction of its operational rotation. As a consequencegrinding media 50 and material 52 to be ground flow substantiallyuniformly around the screen cartridge constituting the separating means42.

In FIG. 11 the inner wall of the hollow end portion 38 is seen todiverge frustoconically away from the open end of the cavity 40. Whenthe agitator shaft 22 is rotating this design has the effect that thecentrifugal forces acting on the grinding media 50 and material 50 to beground generate propelling forces in the direction of enlargement of thecavity 40, in other words away from the open end thereof. Thus the innerwall of the end portion 38 itself presents a conveying member 66. Theseparating means 42 again embodied by a screen cartridge is enlarged incorrespondence with the cavity 40, yet only to a diameter which is alittle smaller than the smallest inner diameter of the cavity 40. Thusthe separating means 42 can be pulled axially out of the end portion 38for replacement, as with all other embodiments.

The conveying members 66 shown in FIGS. 10 and 11 may be combined witheach other.

Exchange of the separating means 42 while the agitator mill is runningyet the pumping means is shut off and without any grinding media 50falling out is provided for in accordance with FIG. 12 by the provisionof a tubular socket 68 at the end wall 36 or a similar closing member ofthe milling body 12. In this tubular socket 68 the separating means 42once more in the form of a screen cartridge is guided in a manner so asto be pulled out. The tubular socket 68 extends into an enlargement 70of the cavity 40, yet it terminates at or just before the beginning ofthe recess 46 so that, during normal operation, it does not impede theflow of grinding media 50 and material 52 being ground through thecavity 40 and the recesses 46.

The stationary tubular socket 68 shown in FIG. 12 may be replaced, asillustrated in FIGS. 13 and 14, by a sleeve 72 guided for axialdisplacement at the end wall 36 and/or a holder 74 fixed to the same. InFIG. 13 the normal operating position is shown at which the sleeve 72does not protrude into the grinding chamber 18 or does so only a little.As shown in FIG. 14, the sleeve 72 may be displaced into a position inwhich it engages in a hollow 76 formed in the end portion 38. Hereby theinterior of the sleeve 72 is separated altogether tightly from thesurrounding cavity 40 and from the grinding chamber 18. The sleeve 72can be fastened in this position so that the separating means 42 isexchangeable while the agitator shaft 22 is running, and yet no grindingmedia 50 or material 52 being ground can flow out.

What is claimed is:
 1. An agitator mill comprisinga milling body (12)which includes a grinding chamber (18) to be filled at least partly withgrinding media (50) and material (52) to be ground and has an inlet (28)for material to be ground and an outlet (30) for crushed material, anagitator shaft (22) having an inner shaft end inside the grindingchamber (18), and a separating means (42) permitting finished pulverizedmaterial (52) to flow out of the grinding chamber (18) to the outlet(30) yet retaining grinding media (50), wherein the agitator shaft (22)has an end portion (38) formed with a cavity (40) therein which is openat the inner shaft end, the end portion (38) of the agitator shaft (22)includes recesses (46), distributed around the cavity (40) and spacedfrom the inner shaft end, through which said grinding media (50) fromsaid grinding chamber (18) may axially flow into the cavity (40) andthrough the inner shaft end to flow back into the grinding chamber (18),and the separating means (42) is arranged at least substantially insidethe cavity (40).
 2. The agitator mill as claimed in claim 1,characterized in that at least one conveying member (66) is formed atthe agitator shaft (22) to promote axial flow of grinding media (50) andmaterial (52) to be ground from the inner shaft end through the cavity(40) to the recesses (46).
 3. The agitator mill as claimed in claim 2,characterized in that the separating means (42) is arranged at leastapproximately coaxially with the agitator shaft (22).
 4. The agitatormill as claimed in claim 3, characterized in that the separating means(42) is arranged on a tube (32) which extends through part of thegrinding chamber (18) from the inner shaft end into the cavity (40). 5.The agitator mill as claimed in claim 4, characterized in that theseparating means (42) communicates through the altogether hollowagitator shaft (22) with the outlet (30) for crushed material disposedat an outer shaft end.
 6. The agitator mill as claimed in claim 4,characterized in that the tube (32) is guided so as to be pulled out tothe exterior in a tubular socket (68) which extends from an end face(36) of the milling body (12) into the cavity (40).
 7. The agitator millas claimed in claim 1, characterized in that the tube (32) is guided soas to be pulled out to the exterior in a sleeve (72) which is arrangedat an end wall (36) of the milling body (12) and is adjustable between anormal operating position in which it is disposed substantially outsideof the grinding chamber (18) and a position for exchange of theseparating means (42), at which position the sleeve (72) protrudes intothe cavity (40) and affords sealing against the agitator shaft (22) in amanner to retain the grinding media (50).
 8. The agitator mill asclaimed in claim 7, characterized in that the cavity (40) divergesfrustoconically away from the inner shaft end.
 9. The agitator mill asclaimed in claim 2 characterized in that the cavity (40) divergesfrustoconically away from the inner shaft end.
 10. The agitator mill asclaimed in claim 9, characterized in that the separating means (42)communicates through the altogether hollow agitator shaft (22) with theoutlet (30) for crushed material disposed at an outer shaft end.
 11. Theagitator mill as claimed in claim 1, characterized in that theseparating means (42) is arranged at least approximately coaxially withthe agitator shaft (22).
 12. The agitator mill as claimed in claim 11,characterized in that the separating means (42) communicates through thealtogether hollow agitator shaft (22) with the outlet (30) for crushedmaterial disposed at an outer shaft end.
 13. The agitator mill asclaimed in claim 11, characterized in that the separating means (42)comprises separating discs (56,58) which are disposed coaxially with theagitator shaft (22) and define an annular gap (60) and of which one isrotatable while the other one is stationary.
 14. The agitator mill asclaimed in claim 11, characterized in that the separating means (42) isarranged on a tube (32) which extends through part of the grindingchamber (18) from the inner shaft end into the cavity (40).
 15. Theagitator mill as claimed in claim 14, characterized in that the tube(32) is guided so as to be pulled out to the exterior in a tubularsocket (68) which extends from an end face (36) of the milling body (12)into the cavity (40).
 16. The agitator mill as claimed in claim 15,characterized in that the tube (32) is guided so as to be pulled out tothe exterior in a sleeve (72) which is arranged at an end wall (36) ofthe milling body (12) and is adjustable between a normal operatingposition in which it is disposed substantially outside of the grindingchamber (18) and a position for exchange of the separating means (42),at which position the sleeve (72) protrudes into the cavity (40) andaffords sealing against the agitator shaft (22) in a manner to retainthe grinding media (50).
 17. The agitator mill as claimed in claim 1,characterized in that the separating means (42) communicates through thealtogether hollow agitator shaft (22) with the outlet (30) for crushedmaterial disposed at an outer shaft end.
 18. The agitator mill asclaimed in claim 17, characterized in that the separating means (42)comprises separating discs (56,58) which are disposed coaxially with theagitator shaft (22) and define an annular gap (60) and of which one isrotatable while the other one is stationary.
 19. The agitator mill asclaimed in claim 17, wherein the separating means (42) comprises ascreen cartridge, characterized in that the separating means (42) isfixed to the agitator shaft (22) and rotates together with the same. 20.The agitator mill as claimed in claim 1, characterized in that theseparating means (42) comprises per se known separating discs (56,58)which are disposed coaxially with the agitator shaft (22) and define anannular gap (60) and of which one is rotatable while the other one isstationary.
 21. The agitator mill of claim 1, wherein at least a portionof said separating means is concentrically rotatable within saidagitator shaft.